G-174 



FUSARIUM-BLIGHT OF POTATOES UNDER IRRIGATION 



BY 



<*&•. 



H. G. MacMILLAN 



H^ 



Reprinted from JOURNAL OF AGRICULTURAL RESEARCH 

Vol. XVI, No. 11 : : : : Washington, D. C, March 17, 1919 




PUBLISHED BT AUTHORITY OF THE SECRETARY OF AGRICULTURE, WITH THE COOPERATION 
OF THE ASSOCIATION OF AMERICAN AGRICULTURAL COLLEGES AND EXPERIMENT STATIONS 



WASHINGTON : GOVERNMENT PRINTING OFFICE : 1919 






_; 



,0* 



FUSARIUM-BLIGHT OF POTATOES UNDER IRRIGATION 

By H. G. MacMiiaan 

Assistant Pathologist, Cotton, Truck, and Forage Crop Disease Investigations, Bureau 
of Plant Industry, United States Department of Agriculture 

HISTORY OF FUSARIUM-BLIGHT 

The Irish potato (Solatium tuberosum) has been one of the most 
profitable crops grown in the Greeley district of northern Colorado. 
In this fertile, irrigated section, one of the oldest in the country, the 
potato gave large yields for many years before any serious setbacks 
occurred. From j9o8 to 191 2 the inroads of disease threatened the 
industry severely, and in 191 1 and 1912 the crops were failures. In 
1 91 5 a laboratory was established at Greeley for the study of potato 
troubles, but since that year the yearly losses have been light. Fusarium- 
blight has been present, however, as a conspicuous malady. 

Fusarium-blight, or potato-wilt, is well recognized in nearly all the 
potato-growing regions of the country, except in the extreme North- 
eastern States. It is caused most frequently by the fungus Fusarium 
oxysporum Schlect., though other species of this genus have been found 
involved. In 1899 l Smith (15) 2 first proved that species of this genus 
would cause plant-wilts, and in 1904 Smith and Swingle (16) described 
a potato-wilt and tuber-rot due to F. oxysporum. It was believed by 
them that the F. solani of Pizzigoni (10) and of Wehmer (27) was iden- 
tical with their species. The confusion which existed over the definition 
of species was largely removed by the taxonomic investigations of 
Appel and Wollenweber (j), Carpenter (2), Sherbakoff (14), and Wollen- 
weber (20). Manns (6), Orton (9), Pratt (11), Wilcox (18), and others 
have continued to reveal the great losses which species of Fusarium 
cause in the potato industry and have suggested methods of control. 

1 Smith, Erwin F. The watermelon disease of the south. (Abstract.) In Proc. Amer. Assoc. Adv. 
Sci. 43d Meeting, 1894, p. 289-290. 1895. 

The following papers are likewise contributory: 

Smith, Erwin F. The spread of plant diseases. A consideration of some of the ways in which para- 
sitic organisms are disseminated. In Trans. Mass. Hort. Soc. 1896, pt. 1, p. 117-133. 1896. 

. The fungous infestation of agricultural soils in the United States. In Sci. Amer. Sup., v. 48, 

no. 1246, p. 19981-19982. 1899. 

s Reference is made by number (italic) to " Literature cited," pp. 301-303. 

Journal of Agricultural Research, Vol. XVI, No. 11, 

Washington, D. C Mar. 17, 1919 

nn Key No. G-i 74 

(279) 



280 Journal of Agricultural Research vol. xvi, No. ix 

PREVALENCE AND LOSS 

Fusarium-blight has not appeared to persist in any one locality. 
Its visitations are sporadic. The losses are, therefore, not to be esti- 
mated in concrete terms. In Colorado in 191 7, a favorable season for 
the crop, about 46,000 acres of potatoes were grown. It is estimated 
that, owing to disease, 10 per cent of the acreage planted gave either 
reduced yield or no yield. In a good field most of the diseased plants 
soon pass out of sight and make no impression on the casual observer. 
Yet these occasional diseased plants probably resulted in a loss of 500,000 
bushels in Colorado alone. At other times the disease spreads more 
generally, and whole fields go down and are lost. Since the part of 
Fusarium spp. in the creation of disease depends largely on environmental 
factors, it is important to note that the conditions which prevail in 
Colorado do not exist in the same way in other places. The descriptions 
of diseases caused by species of Fusarium already published do not, 
therefore, closely apply to Colorado, because the climate, coupled with 
the soil conditions and irrigation practice existing there, creates a condi- 
tion unknown in the East, where most of the work on Fusarium spp. 
has been done. 

DESCRIPTION OF DISEASED PLANTS 

The common manifestations of the disease are a wilting and rolling 
of a few leaves, followed quickly, slowly, or intermittently by the wilting 
of the remainder and usually the premature death of the foliage. Occa- 
sionally a single leaf will wilt, turn yellow, and die, whereas the remainder 
of the plant may continue healthy throughout tlWsjeason. Frequently 
one of the two or more stems of a hill wilts and dies, while the others re- 
main turgid and healthy. The time of appearance varies greatly. It may 
be noticeable when the first leaves appear or at any time throughout the 
season up to maturity. A faint lightening in the color of the plant may 
indicate a gradual attack, and when the attack is severe, a large plant may 
pass from health to complete collapse in two days. Late in the season, 
three or four weeks before frost, plants turgid and unwilted, are found 
upon which all the upper leaves are rolled. They are a little lighter 
in color than normal plants, and have often been.designated by the 
uninitiated as being diseased by leafroll. Plate 4i,B, shows a plant of 
this type; the leaves are rolled, but show no wilting. These plants 
may continue to lighten in color, the leaves to roll, and gradually to 
die. These conditions are due to the presence of Fusarium mycelium 
in the vascular tissues of the stem. Plate 4o,D, shows a plant on which 
the leaves have rolled and are gradually dying. What has actually 
happened in this plant is that the fungus has created a physiological 
drouth which has extended over a long period. Upon examining 
plants in the earlier stages of wilt, the stem and roots are usually found 
clean and apparently healthy, but the seed piece has rotted, and remains 



Mar. 17, 1919 Fusarium-B light of Potatoes under Irrigation 281 

as a wet, jelly-like mass. Later in the season the seed piece practically 
disappears, and the roots and stem may become blackened and decayed. 
At first the stems may be wet and slippery, but in time they become 
dry, brittle, and friable. The main and lateral roots of plants having 
rolled leaves late in the season are often normal in external appearance. 
The term " Fusarium-blight " is preferred for the disease, because it 
is more applicable to all its stages. The name "Potato-wilt" has been 
used elsewhere, and so has "Fusarium-wilt," but their use is likely to 
cause confusion with other diseases, and are not accurately descriptive, 
as they limit the picture to wilt. As will be seen later, the term 
"Fusarium-blight" covers the diseases much more accurately. 

INOCULATION EXPERIMENTS 

The cause of Fusarium-blight is F. oxysporum. Other species of 
Fusarium are capable of producing similar phenomena in the potato 
plant, but F. oxysporum is the species commonly found in isolation 
cultures from diseased material. 

At various times cut potato tubers have been inoculated with spore 
susspensions of F, oxysporum and kept in moist chambers in the laboratory. 
These tubers were always destroyed by the action of the fungus, while 
controls made in the same manner with sterile water remained normal. 

On July 17, 1917, six smooth Early Ohio tubers were given surface 
sterilization. Each tuber was cut into two equal parts, one half being 
reserved for control and the other half for fungus inoculation. Glass 
rings of the Van Tieghem cell type were smeared on the edges with 
petrolatum and put down on the center of the cut surface of the tuber 
after it had dried slightly from cutting. Two drops of a heavy spore 
suspension from an authentic pure culture of F. oxysporum were placed 
within the ring under aseptic conditions, and the cell closed with a cover 
glass. The controls were prepared the same way with sterile water. 
These seed tubers were taken to the field and planted in a row at a depth 
of 3 inches, where they were subjected to natural field conditions rather 
than to the artificial environment of a flat. On August 13, 1917, twenty- 
seven days after inoculation, the ground was carefully scraped away and 
the plants taken up. The six seed pieces inoculated with the fungus were 
badly decomposed. Four of them had disintegrated to a completely 
rotten mass. The other two had sprouted, and a small firm area remained 
by the stem. F. oxysporum was recovered from these in pure culture. 
The controls were uniformly healthy throughout. Plate 37, A, illus- 
trates a control and a diseased seed piece of this experiment. 

On August 10, 1 91 7, fifteen tubers were cleaned and sterilized. They 
were cut as before, and one half of them were inoculated with a spore 
suspension of F. oxysporum dropped into glass rings, the other half being 
treated as controls. Five inoculated and five control seed pieces were 
planted together in sterilized soil in each of three flats. The}- were 



282 Journal of Agricultural Research vol. xvi, No. n 

watered with sterile water. The flats were set on the edge of a field, 
where ordinary weather factors would act as normally as possible. These 
flats were noted finally on September 8, 1917. The control plants were 
healthly throughout, with normal foliage and stems 10 inches long. In 
the first flat only one tuber of the inoculated seed sent up a pair of sprouts. 
One of these was dead and the stem blackened for 2 inches above the 
ground. Although the seed piece was thoroughly decayed, the other 
sprout appeared healthy, as shown in Plate 37, B, It is characteristic 
in every respect of the field blight. A closer view of the seed piece, 
together with a control seed piece from the same flat, is shown in Plate 
37, C. In the second flat two seed pieces failed to germinate, owing to 
decay. One was dead, and the stem was blackened. In the third flat 
one seed piece failed to germinate, while four sent up sprouts. These 
had all wilted thoroughly, though death had not yet occurred. None of 
these plants had been subject to frost. Isolation cultures were made 
from all the diseased plants from the three flats, and F. oxysporum was 
recovered in pure culture in each case. 

On September 9, 191 7, three flats were prepared for inoculation. 
Sterile soil was used. Seed pieces of the Pearl variety were inoculated 
with a spore suspension of F. oxysporum in the usual way. The spore 
suspension was made from cultures taken from the diseased seed pieces 
of the inoculation experiment of July 17. No controls were made, 
because of lack of space. Owing to the lateness of the season, these 
flats were taken to Fort Collins, Colo., where, through the courtesy of the 
Horticultural Department of the Agricultural College, they were placed 
in the greenhouse. The plants were not seen until November 3, at 
which time all were dead with the exception of three plants, then about 
to die. 

On August 13, 1 91 7, nineteen whole tubers which had been planted in 
the field for three weeks and which had sent up sprouts were inoculated. 
Fourteen of them were inoculated with a spore suspension of F. oxysporum 
poured into glass tubes entering the epidermis of the tuber; five were 
treated with sterile water as controls. In each case the plant had a 
healthy, vigorous start. On September 9 the plants were taken up and 
examined. The seed pieces of the controls were sound and the plants 
healthy; seven inoculated plants were healthy, though the seed piece 
was decayed; the other seven were wilted, the stem was blackened, and 
the seed piece was thoroughly decayed. 

On August 10, 1 91 8, sixty-one plants planted in sterile soil in flats were 
inoculated with F. oxysporum. Sixteen plants in flats in sterile soil were 
treated as controls. The method of handling was different from that 
used before. The seed pieces had been planted with the cut surface 
turned up, about a month previously, and the flats left in a cool place. 
They were watered periodically with sterilized water. By August 10 the 



Mar. 17, 1919 



Fusarium-Blight of Potatoes under Irrigation 283 



plants had germinated and sent up strong, vigorous sprouts. The seed 
pieces were solid and unusually well calloused. For the purpose of inocu- 
lation the soil was scraped away, and a small core about 1 cm. long was 
taken out of the upper surface of the seed piece with a small coring tool. 
The pit made by the removal of the core was filled with a spore suspen- 
sion of F. oxysporum and closed with a cover glass smeared with petro- 
latum. The controls were treated in the same manner, except that the 
pit was filled with sterile water. For the next 20 days the flats were ex- 
posed to approximately field conditions. The experiment was discon- 
tinued on August 30. At that time the inoculated plants had wilted 
to the ground, while the control plants were normal. Upon examination 
of the underground parts of the inoculated plants the seed pieces were 
found to be wholly decayed, and the main root was infected. The roots 
were not destroyed nor was the main root decayed, but the vascular 
tissue was woody and filled with mycelium. Isolation cultures made 
from 40 of the inoculated plants gave F. oxysporum in pure culture. 

INOCULATIONS ON MATURE PLANTS 

On August 13, 1 91 7, inoculations were made on Early Ohio potato 
plants in the field for the purpose of approximating the disease in its 
mature stage. The plants were in good soil and had shown no signs of 
blight from natural infection, though the seed pieces had been attacked. 
The method employed was very simple. The soil was carefully scraped 
away from the stem to a depth of 3 or 4 inches, and a slit was made with a 
scalpel lengthwise through one stem of the plant. A wedge of melilotus 
stem upon which F. oxysporum had been cultured, and which bore my- 
celium and spores plentifully, was inserted in the slit, and the whole being 
covered with soil. Forty-six plants were inoculated with the fungus, 
and 26 were treated as controls. On September 18 these plants were 
taken to the laboratory for examination. All of the plants had two or 
more stems, but in the case of the plants inoculated with F. oxysporum 
only the treated stem showed any injury. The plants treated as controls 
recovered from the mechanical injury, and the wound healed. Plate 
38, B, shows a control plant and the method of inserting the wedge. Of 
the inoculated plants 3 were lost, 4 showed no infecdon, 2 showed weak 
or doubtful infection, and 37 showed positive infection. Stems showing 
infection were typical of the natural blight in every respect. The stems 
were dead, blackened, and shattered in most cases. Plate 38, A, illus 
trates two stems of the same plant; the stem at the left was inoculated; 
the one at the right was not, and shows no injury. Of the 37 stems show- 
ing positive infection 20 were selected at random and isolation cultures 
made. These yielded pure cultures of F. oxysporum in 18 cases, the 2 
others being badly contaminated. 



284 Journal of Agricultural Research vol. xvi, No. » 

MODE OF INFECTION 

Hitherto infection of potato plants by F. oxysporum through the root 
hairs and small rootlets has been accepted as the usual method. Smith 
and Swingle (16, p. 13) said this occurred, and Manns (<5, p. 306) reasserted 
the fact. In case of the cowpeas and cotton, Orton (7, p. 10; 8, p. 8) 
found this manner of infection in both cases. Cromwell (5, p. 4.25) sup- 
posed root infection to be the means of entrance of Fusarium trache- 
philum Smith, causing the wilt disease of soybean. Jones and Gilman 
(4, p. 7) found the roots of cabbage to be attacked by Fusarium. These 
numerous instances would call for careful examination of the roots of in- 
fected plants. During the years 191 6 and 191 7, in only 6 plants out of 
many hundreds examined was this method of infection determined as 
probable in the case of fusarium-blight of the potato in the Greeley dis- 
trict. In 1 91 8 the soil temperature at a depth of 6 inches was 6° F. above 
the average for the month of June of the preceding two years. Plants 
of the Charles Downing variety, planted during the last of May or early 
June, were badly diseased in some fields by being attacked through the 
fine roots and root hairs by F. oxysporum. This one variety was more 
severely attacked than any other, even in fields containing several varie- 
ties. Most other varieties were not assailed in this manner at all, except 
a few scattering Early Ohio plants. Higher temperatures seem to be 
necessary for root infection. 

Infection from seed tubers containing the Fusarium organisms in the 
vascular bundles has been very seldom found. Wollenweber (10, 20) has 
shown that F. oxysporum overwinters in potato tubers, where it causes 
the familiar vascular discoloration. With the sprouting of the eyes when 
the seed piece is planted the organism infects the new plants and pre- 
sumably causes wilting and death. One of the most extensively advo- 
cated control measures has been aimed to avoid this kind of infection. 
No trouble has been experienced with this method of infection in the last 
three years. Field experiments tending to show the nonseverity of this 
method of infection will be given below. 

SEED-PIECE INFECTION 

In the Greeley district and in other parts of Colorado potato seed pieces 
become infected with the Fusarium organism from the soil. The cut seed 
is vastly more liable to attack than the whole seed, and the decay follow- 
ing infection will begin two or three days after planting. It is justifiable 
to assume that in the average field nearly all cut seed pieces are infected. 
Fields have been examined in which hundreds of seed pieces were dug a 
few days after planting, and less than 5 per cent were found to be free 
from infection. The infection occurs through the large open wound of the 
cut surface, lightly protected by callus. The interior loose parenchyma 
at the center of the tuber, farthest from the active tissue of the vascular 



Mar. X7. 1919 Fusarium- Blight of Potatoes under Irrigation 285 

region, is the weakest and least protected. There is a difference in the 
susceptibility of seed of different varieties, but what seems more im- 
portant is that seed of the same variety from different sources varies 
greatly in its power of resistance. The rot following infection may be 
swift, and the fungus will destroy the seed piece before germination 
begins. 

Plate 37, E, illustrates a seed piece upon which no eye has germinated, 
though the piece is nearly destroyed by rot. In this illustration two dark 
spots are to be noted in the vascular region, denoting vascular infection; 
yet no decay originated at that point. When the decay is slower, the 
seed germinates and sends up a vigorous shoot. Plates 37, D, and 38, f^C- 
illustrate cases of germination followed by seed-piece rot. The region 
adjacent to the active tissue is the last to decay because it is more resistant 
and because the decay begins in the loose parenchyma and advances 
toward the germinating point or place of attachment of the shoot. Where 
decay is delayed sufficiently to allow germination to take place, the decay 
works slowly through the active region, or it may stop temporarily. 
Plate 37, D, illustrates how the decay is delayed nearest the growing part 
and how it advances evenly toward this region. Plate 39, D, illustrates 
the base of a plant the seed piece of which had decayed thoroughly. The 
stem is cut away, showing the healthy tissue within and the absence of the 
parasite. The general good health of the roots should also be noted. 

Some plants appear to grow normally for a few weeks, after which 
symptoms of disease begin to appear. The color may or may not change, 
and the leaves may show curling, rolling, or wilting. One lower leaf may 
turn yellow, wilt, and fall, while the remainder of the plant is a picture of 
health. In a single hill containing two or more sprouts the tip of one 
may wilt and the other remain healthy. Plate 40, C, represents a plant 
consisting of two stems, one of which is healthy, the other wilting. The 
stem at the left will die, while the stem at the right may live through the 
season and yield normally. Upon taking up such a plant the decay of the 
seed piece will be shown to have advanced toward and into the wilted 
stem, while in all cases the root system is healthy in every branch. 
Plate 40, B, shows the top of a plant consisting of three stems. The top 
leaf and the one below it on the same stem are wilted. Neither the other 
leaves nor the color of the plant indicated anything abnormal. Plate 
39, C, shows the seed piece and the three stems of the tops illustrated in 
Plate 40, B. The wilted leaf shown in Plate 40, B, is on the middle stem 
pictured in Plate 39, C, which is at the center of the decay. The stem at 
the left, healthy on Plate 40, B, is here shown with a slight spund area 
remaining in the seed piece. A stem which shows these symptoms in 
early summer when conditions are favorable may not at once succumb, 
but is usually doomed to an early death. Plate 39, B, shows a young 
plant in which the decay advanced continuously from the seed piece into 



286 Journal of Agricultural Research vol. xvi, no. n 

the stem. Many plants are to be found which show the violent symp- 
toms, wilting, drooping, and death, within a few days. 

The great majority of plants in a field may advance to late maturity 
with no visible signs of Fusarium-blight. Entire fields have been ob- 
served which showed natural wilting caused by delayed irrigation; wet 
periods may occur, owing to excessive rain following an irrigation; and 
either of these conditions are conducive to the increased activity of the 
fungus, though recovery is possible and often occurs. In an entirely 
healthy field at any period of the season conditions may arise in which the 
blight gains the ascendancy, the plants wilting and dying in the course of 
a week. This may happen as late as September, yet infection did not 
occur immediately before the appearance of wilt, as the fungus had been 
present since the time of planting. 

Whole seed is protected by a sound epidermis underlain by an active 
vascular tissue, the best protection the seed may have. Whole seed 
germinates quickly and establishes a sound, vigorous plant weeks before 
the seed piece has been destroyed by fungi, and the plant becomes liable 
to attack. It is not unusual for whole seed to remain sound through the 
growing season, though the ultimate death of the nongerminated eyes, 
the worn-out vitality of the vascular region, and the dead epidermis make 
infection possible. Injuries in handling or planting, such as are received 
from picker planters, render infection comparatively easy. Clipping the 
stem end to inspect for vascular infection is a most reprehensible practice, 
as it breaks the epidermis and makes a wound in that part of the tubeJ7 
tissue which is lowest in vitality and least in the power of self -protection. 

OCCURRENCE OF THE CAUSAL FUNGUS 

In the case of seed pieces which obtained a favorable start and sent up 
sprouts the decay is slow. In individuals where it takes weeks to decay, 
the decayed watery portion leaches away and a callus forms when the 
growing tissue is reached. Where field conditions are right, the fungus 
will continue its slow advance into the foot of the stem, causing no decay 
and slight or no discoloration. As conditions unfavorable to the plant 
arise, the fungus grows in the vascular bundles and causes discoloration. 
Plate 39, B, shows a 6-weeks'-old stem to the left portion of which the 
decomposed and dried piece clings. Discoloration of the pith is found 
only at the very foot of the stem, and the upper vascular bundles are free 
from any trace of the fungus. In the field this plant would be regarded 
as healthy. In plants of this type the lowest roots on the stem are cut 
off from supplying water, and thereby cause some of the temporary 
queer symptoms to be noted in the foliage. The plant may recover, 
draw on the roots above more heavily, and continue growth. Nothing 
more may happen throughout the season; harvest may arrive, and the 
plant yield normally. In other cases where the soil is wet and compact 
the fungus is more active; it decays the foot of the stem, cuts off stolons, 
decays new potatoes, and finally kills the plant. Plate 39, A, pictures a 



Mar. 17, 1919 



Fusarium-Blight of Potatoes under Irrigation 287 



plant taken from a field where irrigation water got beyond control and 
flooded a portion of the field. The fungus advanced rapidly, decayed 
the stem, and caused the death of the plant. The advance was so rapid 
that the roots were killed for only a short distance, remaining uninfected 
2 inches from the stem. In severe cases action is rapid and universal; 
whole fields succumb, causing the well-known epidemics. When .stems 
of rapidly killed plants are pulled up, they are black, soft, and wet, as is 
illustrated in Plate 38, D. This plant, naturally infected by F. oxyspo- 
rum, is strikingly like the plant shown by Link (5, fig. 7), as caused by 
artificial infection with this organism. Other organisms follow closely 
behind the species of Fusarium and complete the decay of any tissue not 
thoroughly invaded by that fungus. 

ISOLATION OF CAUSAL ORGANISMS 
During the growing seasons of 191 6, 191?, and 191 8 more than 1,500 
cultures have been made in attempts to isolate the causal organisms. 
Plants in every condition, from newly planted diseased seed to new 
tuber infection at harvest, were used as sources of culture. The material 
was selected in the field, and taken at once to the laboratory. It was 
carefully washed under slowly running water and patted to comparative 
dryness between damp towels. The material was prepared for culturing 
by breaking it open and, with a sharp chisel-pointed platinum needle, 
transferring small pieces from the desirable areas to tubes containing 
sterile melilotus stems. 

In making these cultures too many precautions can not be taken to 
keep within very small areas with the needle. The line of demarcation 
between apparently firm tissue and diseased tissue is definite and narrow. 
Cultures made from the firm tissue immediately before the line, and on 
the line, were usually pure, and sporulated readily. Tissue back of the 
line gave many contaminations; too far in advance gave no growth at all 
in culture. In decaying seed pieces it is well to keep within 2 mm. of the 
line of decay. In the green tissue of growing stems little trouble will be 
experienced if the stems are not broken or torn before culturing; and, 
as infected stems soon become woody, a stiff sharp needle is necessary 
in culturing from them. Any blackened tissue will usually yield a cul- 
ture. These infected tissues invariably yield species of Fusarium, 
though, if decay has advanced to the point of disintegration, contami- 
nating 'organisms will be present. Stysanus stemonitis is frequently 
found* in both attacked stems and seed pieces. Bacteria are rarely 
found in firm or semifirm tissue. 

FIELD EXPERIMENTS 
A series of experiments were performed with several lots of potatoes 
to determine as nearly as possible the origin of the disease developing 
during the growing season, basing the deductions upon the conditions 



288 Journal of Agricultural Research voi. xvi, No. » 

of the seed at planting time and the symptoms displayed during growth. 
These experiments were carried out in the field under conditions approxi- 
mating commercial field practice, and no methods of culture or treatment 
were used at any time after planting which would not have been used 
by a commercial grower. For the purpose of this experiment it was 
conceded that parts of the same seed potato, grown under like condi- 
tions, would follow within reasonable limits pretty nearly the same course 
of procedure in growth, disease symptoms, and general appearance. A 
difference in two plants from twin seed pieces' must be accredited to 
different conditions encountered during the growing season after planting. 
Various lots of seed were assembled in 191 6 to test out this assumption. 
Among others, they consisted of one lot of certified Wisconsin Pearl, 
one lot of certified Wisconsin Rural, two lots of Early Ohio from the 
Red River Valley in Minnesota, one lot of Rural from the Carbondale 
District of Colorado. 

All tubers were cut from bud to stem end, dividing the tuber into two 
equal parts. All tubers above 6 ounces werecut into four pieces. These 
were cut in the field and planted immediately side by side in parallel 
adjacent rows. They were given as good care as possible during the 
growing season. The summer was excessively warm until July 30, 
1 91 6, at which time 3.09 inches of rain fell. The remainder of the sum- 
mer was comparatively cool. Notes were taken four times during the 
summer: Once when the plants were about 6 inches high, then when 
they averaged 12 inches high, again when they were full grown, and 
finally when no normal change was to be expected. No reference was 
made to any previous note; other members of the force were asked to 
assist in the work, and every method employed by which an impartial 
diagnosis could be made. 

KEY TO TABLE I. 

Pbr the purpose of summarizing and presenting the performance of these lots of 
tubers, a new form of table, known as an aggregation table, has been constructed. 
This table must not be confused with a correlation table, which it resembles in general 
appearance, but not in context. In any single row of potatoes six different ultimate 
types of plant were recognized. These have been designated as " H, " " HD, " " DH, " 
"D," "A," and "O." The meaning of these symbols are as follows: "H" denotes a 
plant which appeared healthy throughout the growing season; "HD" denotes a plant 
which was healthy during the first part of the season, but finished by being diseased; 
"DH" denotes a plant which gave manifestations of disease during the first part of 
the season, but finished by being healthy; "D" denotes a plant which was diseased 
throughout the season; "A" denotes a plant so badly diseased as to be merely existing, 
with no hope of progeny; "O" denotes no germination, or a case in which the seed piece 
suffered the maximum of disease and rotted in the ground. All plants in a row fell 
into one of these divisions. In comparing the plants from twin seed pieces in the two 
adjacent rows at the same time it is seen that in classification certain coincidences, or 
lack of them are significant. In the case of some plants classed as "H" in one row, 
the twins in the adjacent row were "H" also; in more cases the}* differed for all the 



Mar. i 7> 1919 F us ar turn- Blight of Potatoes under Irrigation 



289 



other five groups. Originally in numbering rows in the field the even and odd fol- 
lowed naturally, so that in the tables the parallel adjacent rows are most easily desig- 
nated by the terms "even" and "odd." In the tables the "even" rows are read 
vertically — that is, the designating letters are placed across the top, and the aggregate 
totals for each class across the bottom; the "odd" rows are read horizontally, the let- 
ters at the left and the aggregate totals at the right. However, as noted before, many 
of the twins differ individually in their performance, so that in order to express this 
deviation the total of one class in one row is split up according to the numbers required 
to express the reciprocal in the other row. A concrete example is given in Table 1 A. 
In the even row there are 352 H, 4 HD, 5 DH, 1 D, 13A, and 12 O plants, a total of 387. 
In the odd row there are 320 H, 5 HD, 7 DH, 1 D, 23 A, and 31 O plants, a total of 387. 
In comparison with 352 H plants in the even row, twin for twin in the odd row, 296 
plants are also H, while 4 are HD, 7 DH, 1 D, 20 A, and 24 O. Turning about, it is 
seen that, of the 320 H plants in the odd row, twin for twin in the even row, 296 are 
H, 3 HD, 3 DH, 1 D, 11 A, and 6 O. The same system follows for the other classifi- 
cations. It is revealed, then, how nearly alike twin seed pieces perform, for where 
they are alike the numbers appear in either the HH, HDHD, etc., squares down to 
00. Differences are shown when they appear elsewhere. 



Table I. — Aggregation of seed piece performance of Irish potatoes 

A. — WISCONSIN PEARL 

[1 equals 0.258398 per cent of 387] 





H 


HD 


DI-I 


D 


A 


O 


Total. 




No. 


Per 

cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


H 


296 

4 

7 

1 

20 

24 


76. 49— 

I.OJ + 

I. Sl- 
oe- 
s' I7~ 
6. 20+ 


3 

1 


0.78— 
.26- 


3 


0.78— 


1 0. 26— 


11 


2.84+ 


6 


1-55+ 


320 
S 
7 


82. 69— 


HD 




DH 
















1.81- 


D 




















.26- 


A 






2 


.52— 




2 


•52— 


1 
5 


.26— 

1.29+ 


23 
31 




O. . 


8.014- 
















Total . . . 


352 


90. 96 — 


4 


1.03+ 


5 


1. 29+ 


1 . 26— 


13 


3-36— 


12 


3.10+ 


387 


100.00 



B. — INFECTED WISCONSIN PEARL 
[1 equals 3.70370 per cent of 27] 



H 


23 

1 
1 


92. 60— 
3- 7°+ 
3-7°+ 










j 










HD 






















DH 












1 






















:::::::::::: 





















































































27 


100 00 



















































C. — CERTIFIED WISCONSIN RURAL NEW YORKER 
[1 equals 0.225225 per cent of 444] 



H 


89 


20.05— 


1 0.23— 


24 


5-41 — 


1 


0.23— 


19 


4.28— 


3° 


6.76- 


164 


36. 94— 


DH 


16 


3.60+ 




32 

2 
II 
19 


7. 21 — 

•45+ 
2.48- 
4.28- 


2 


•45 + 


14 


3-15 + 


16 


3.60+ 


80 

2 

44 

154 


18.02— 


D . 




•45+ 


A 


18 
67 


4-°5+ 
15.09+ 




2 

4 


•45 + 
.90+ 


23 


•45 + 
5-IS+ 


II 

40 


2. 48 — 
9. 01 — 


9.91 — 


O 


1 | -23— 


34- 68+ 






Total . . . 


190 42. 79+ 


2 


•4S + 


8S 


19.82— 


9 


2.03 — 


58 


13. 06+ 


97 


21.85- 


444 


roy- co 



290 



Journal of Agricultural Research 



Vol. XVI, No. 11 



Table I. — Aggregation of seed piece performance of Irish potatoes — Continued 

D. — INFECTED CERTIFIED WISCONSIN RURAL NEW YORKER 
[1 equals 6.25 per cent of 16) 





H 


HD 


DH D 


A 


O 


Total. 




No. 


Per 
cent. 


No. 


Per 
cent. 


xt Per 
No - cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


H 


6 


37-5° 






1 6. 25 








6. 25 


1 


6.25 


9 
















DH 


1 


6.2s 






1 6. 25 










1 


6. 25 


3 18. i< 




















A 


1 
2 


6.25 
12. 50 




















1 

3 




O 














1 


6.25 


18-75 


















10 


62.50 






2 12. 50 






1 


6. 25 


3 


18.75 


16 

















E. — RED RIVER VALLEY EARLY OHIO. 
[1 equals 0.259067 per cent of 386] 



H 


141 

2 

29 

X 

7 
62 


36.53— 

•52— 
7-5I + 

•52— 
1.81 + 
16.06+ 


a 


0. 52— 


25 


6.48- 




14 


3-63— 


37 
I 
6 


9-59— 
.26- 

1-55+ 


219 

47 
3 
12 

102 


56- 74— 
•78— 


HD 




DH 






11 


2.85- 




I 


.26- 


12. la- 


D 






I . 26 — 


va- 
s' «— 


A .. 






! 


I 
3 


.26— 
.78- 


4 
20 


1.04— 
5- 18+ 


O. .. 


1 


.26— 


16 


4. 14+ 






Total . . . 









243 


62.95 + 


3 


.78— 


52 


13-47 + 


I 


.26— 


19 


4.92 + 


68 


17.62— 


386 


100.00 



F. — INFECTED RED RIVER VALLEY EARLY OHIO. 
[1 equals 2.857142 per cent of 35] 



H 


16 


45-71 + 






4 


11-43 — 






2.86— 


2 


5-71 + 


=3 




HD 












DH... 


2 


5-71 + 


















2 


5-71 + 


D 


















A 


















1 
2 


2.86- 
5-71 + 


I 

9 


2.86— 


O 


4 


11-43 — 


I | 2.86- 




C. 71 + 














.... 








Total . . . 


22 


62.86- 


1 2.86— 






2.S6- 


5 


14.29— 


35 














1 





G. — CARBONDALE RURAL NEW YORKER 
[1 equals 0.3125 per cent of 320] 



H... 




29 


9.06+ 




29 


0.06+ 


1 


0.31 + 


5 


1-56 + 


27 


8.44+ 


91 


28.44— 


HD. 






DH .. 


10 


3- 12 + 




40 
2 
8 

39 


12.50 
. 62 + 
2.50 
12. 19 


1 


•31 + 


3 


-94— 


16 


5.00 


70 

2 

24 

133 


21.88— 


D... 




.62+ 


A 


5 
29 


1-56+ 
9.06+ 




1 
1 


■31 + 

•31 + 


1 
10 


•31 + 
3- 12 + 


9 
53 


2.81 + 
16. 56+ 


7-5° 


O 


1 J -31+ 




Total.... 






73 


22.81 + 


I 


•31 + 


118 I36.87+ 


4 


1.25 


19 


5-94— 


i°S 


32.81+ 320 


100.00 



H. — GREELEY LATE OHIO. 
[1 equals 1.111111 per cent of 90] 



H 


45 
I 
6 


50. 00 1 


1. 11 + 


7 


7.78- 


| 


3 


3-33 + 




c.cfi- 


61 

I 
14 


67. 78- 
I.II + 


HD 






DH 


6.67+ 




6 


6.67+ 








2 2. 22 — 


I5-56- 


D .. 












A 


1 
7 


1.11+ 




1 
2 


1. 11 + 

2. 22+ 










2 

12 


2 22+- 


O. .. 


7. 78— 










3 | 3-i3 + 


13-33 + 




Total.... 














60 


66.67- 1 


1. 11+ 


16 


17.78- 






3 


3-i3 + 


10 


II. 11 + 


9C 


IOO 00 











Mar. 17, 1919 Fusarium- Blight of Potatoes under Irrigation 



291 



Table I. — Aggregation of seed piece performance of Irish potatoes — Continued 

I. — INFECTED GREELEY LATE OHIO 
[1 equals 1.960784 per cent of 51] 





1 
H HD 


DH D 


A 


O 


Total. 




No. 


Per !„ Per 
cent. ™° m \ cent. 


No. 


S N °- 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 
cent. 


No. 


Per 

cent. 


H 


26 


50.98+ 1 1.96+ 


2 


- H-l 




2 


3.92+ 


2 


3-92 + 


33 




HD 








DH 


4 


7.84+ 






5 


9- 80+ 1. 












9 




D 




















A. . . 








1 
1 














1 
8 


1.96+ 
15.69- 


O 


6 


11. 76+ 






1.96+ 1 








1 


1.96+ 
















Total.... 


36 


70- 59- 


1 


1.96+ 


9 




2 


3-92+ 


3 


S-88+ 


Si 






5 l""| 





J. — GREELEY PEARL 
[1 equals 0.7246377 per cent of 138] 



H 


63 45-65+ 
1 .72 + 
4 2-90— 


6 
2 


4-35 — 

1-45- 


4 


2.90— 






4 


2.90— 


11 

1 
2 
1 
3 
13 


7-97+ 
.72 + 

1.45— 
• 72 + 

2. 17+ 

9.42 + 


88 
4 
6 
1 
11 
28 


63-77— 


HD 






DH 










4-35— 

.72+ 

7-97+ 


D 














A 


5 3-62 + 
10 J 7.25— 


1 
2 


.72 + 
1-45- 






2 

3 


1-45— 

2. 17+ 


O 


...J 












Total.... 


83 J60. 14+ 


11 


7-97 + 


4 


2.90 — 






9 


6.52 + 


31 


22-46+ 


138 













K. — INFECTED GREELEY PEARL 
[1 equals 1.8867924 per cent of 53] 



H 


22 


41. SI- 


3 

1 


S-66+ 
1.89— 




s. 664- 






4 7-55 — 


6 




38 
1 


7.170— 
1.89— 


HD 










DH... 


















D 








; 


.... 






1 
1 


1.89- 
1.89— 
i:.66+ 


1 
6 

7 


1.89— 


A 


3 
3 


S' 66+ 
5-66+ 










2 3-77 + 
I 1 1.89— 




O 




|....| 





















Total. 


28 


52-83 + 


4 


7-55- 


3 


5-66+ 






7 13.21 — 





















L. — INFECTED COLORADO PEARL 
(1 equals 0.6666666 per cent of 150] 



H 


"5 
'4 


76.67- 
9-33 + 


14 
5 


9-33 + 
3-33 + 






| 1 




T.*5 + 


I.? I 
19 


87-33 + 


HD 








' 




DH 


















D 




























A 




























O 



















































Total... 




19 


12.67 — 










ISO 














1 1 1 









M. — IDAHO-GROWN IDAHO RURAL 
[1 equals 0.826446 per cent of 121] 



H 


105 
5 


86- 78- 
4-13 + 




















t.6;4- 


- 


95-87- 
4-13+ 


HD... 


















DH... 


















D.... 




















A 






















O 




















Total.... 






















no 


9 


7-44— 






1 


2 


I-6 5 + 


121 


100 00 








1 


I""l 





292 Journal of Agricultural Research vol. xvi, No. h 

WISCONSIN PEARL (TABLE I, A-B) 

Aggregation Table I, A, illustrates the performance of the certified 
Wisconsin Pearls potatoes in 191 6. There was a total of 774 seed pieces 
planted, the result of dividing 387 tubers. The striking thing to be 
nor.ed in this section of the table is the fact that with the majority of 
diseased plants in either row the twin was healthy. In only 1 1 cases did 
both twins fall outside of a healthy square, five of these being in the 
square 00. If vascular infection was to act here only the 5 twins in the 
00 square could properly be said to come under control of it, because it is 
the only instance where the performance was the same for both twins. 
In the cases of the 80 pairs of twins, 1 of which was in some way diseased 
and the other healthy — that is, those in both rows where 1 twin was 
an H plant, exclusive of those in HH — it must be regarded that the 
disease was newly contracted. Before planting, all tubers were cut at the 
stem end to inspect for vascular discoloration, indicating the presence 
of a possible disease organism. Cultures were made from diseased 
tissue. Only 27 tubers, or 6.98 per cent, showed any discoloration. 
Tabulating then according to the place the tuber occupies in Table I, A, 
their places are shown in Table I, B. 

According to the old conception of the danger of planting diseased seed, 
the 27 tubers, planting the 54 plants here shown should have given some 
sign of disease. The 2 which fall without the HH square are healthy 
plants, for one-half of the tuber would indicate no tendency to disease be- 
cause of the vascular parasite, but because field conditions acted as in 
the case of 78 similarly situated plants, as shown in Table I, A. 

WISCONSIN RURAL (TABLE I, C-D) 

The certified Wisconsin Rural potatoes were treated in the same manner 
throughout, and were tabulated in the same way: 444 tubers were used, 
planting 888 hills, and their performance is shown in Table I, C. 

The plants in this table are well distributed except in the HD columns. 
The performance of the twins as representing the strictly inherent ten- 
dencies of the tuber seems not to be indicative of any considerable failure 
because of previous faults. There are 40 pairs in 00, and 30 and 67 
pairs in HO and OH, respectively. The factors which placed the 40 
pairs in 00 did not act on them as parts of 40 tubers, but as 80 individual 
plants, the same as took place with the 30 and 67 pairs, one-half of which 
were healthy. This variety is peculiar in showing such a contrast be- 
tween susceptibility to disease and vigor to survive and grow away from it. 
The tubers of this lot were planted within 10 feet of the lot represented 
in Table I, A. 

Table I, D, represents the place in which those seed tubers fell which 
showed discoloration in the vascular system. These 16 tubers (3.60 + 




Fusarium- Blight of Potatoes under Irrigation 293 



per cent) are placed in the table according to the place they occupy in 
Table I, C, and it is regarded as of no significance that they fall where 
they do. 

EARLY OHIO (TABLE I, E~F) 

The Early Ohio seed obtained from the Red River Valley consisted of 
two lots. These lots were grown separately, but their performances were 
so nearly alike that they have been combined and presented in Table I, 
E, as one lot. 

This table shows plants falling in the DHDH, DD, AA, and 00 squares, 
a tendency not noted in the previous tables. In the case of the plants 
falling in DHDH, it would appear that some special weakness had devel- 
oped in the 22 plants grown from these 1 1 tubers which placed them there. 
Inherent weakness, then, can not be predetermined by mere examination 
of the tubers, because Table I, F, which represents the location of the 
tubers showing vascular discoloration (9.07 — per cent), placed according 
to their location in Tables I, E, has none represented in DHDH. These 
plants outgrew their earliest diseased condition, and finished the season 
in apparent healthy condition. Table I, E, does not indicate, however, 
any strong vigor on the part of this lot. 

Table I, F, represents the place the 35 tubers of Table I, E, which 
showed vascular discoloration fell, placing them according to their loca- 
tion in Table I, E. 

RURAL NEW YORKER (TABLE I, G.) 

One lot of seed of the Rural New Yorker variety was obtained from 
the Carbondale District of Colorado. It consisted of 320 tubers, free 
from vascular discoloration, and was regarded as stock of superior quality, 
selling at an advanced price. Table I, G, illustrates the almost complete 
failure of this seed through seed-piece infection and rot in the Greeley 
District. 

In this table, where so much disease is represented, the conspicuous 
absence of plants falling in the HD columns (1 in the even row), and 
in the DD square, is significant. Root infection did not occur; no vascular 
discoloration was present in the seed. The great preponderance of 
plants in the 00 square and the O columns, shows clearly that a most 
serious inherent weakness is present in the seed to withstand infection 
from the soil. The number of plants that did not eventually become 
healthy, having previously grown and been diseased, are very few. 
There is a strong tendency to die or survive (H or DH), for the plants that 
are H or DH were vigorous at the end of the season. The others either 
failed, as in O, or gave evidence of a gradually declining health, as in 
D and A. The lack of plants in the HD columns (1 in the even row) is 
further evidence that a healthy plant maintains its position. 



294 Journal of Agricultural Research vol. xvi. No. « 

LATE OHIO DISEASED SEED (TABLE I, H-l) 

In the fall of 191 5 several fields were visited for the purpose of staking 
diseased hills of potatoes. The hills selected all showed blackening of 
the stems and death of the tops, with many cases of rot in the tubers. 
At harvest the badly decayed tubers were discarded for the reason that 
they were in no condition to keep through the winter. The tubers 
showed a large percentage of vascular discoloration, and the remainder 
were believed to be infected, though not seriously. All came from hills 
affected by Fusarium-blight. Cultures were made from the stem end of 
all showing discoloration, and all yielded species of Fusarium. The 
tubers were cut and planted as twins in adjacent rows and given the same 
culture as the lots mentioned above. Table I, H, shows the performance 
of such seed of the variety Late Ohio in the year 1916. 

The complete absence of any plants falling in the D columns is the 
outstanding feature of this table. At best, only the 6 pairs represented 
in DHDH square could be said to show the results of vascular infection, 
especially from the occurrence of 5 of them in the DHDH square in Table 
I, I. Compared with Table I, E, which represents a healthy Early Ohio 
variety, the advantage in health is with the home-grown seed. 

A table representing the places in which the 50 tubers (56.66 -f- per 
cent) showing decided vascular discoloration fell, is shown by Table I, I. 

PEARL DISEASED SEED (TABLE I, J-K) 

One lot of diseased seed consisting of 138 tubers, Pearl variety, acquired 
in the same manner as the Late Ohios, were cultured from the stem-end, 
and planted under the same conditions as other lots. Table I, J illus- 
trated the performance of this badly diseased seed stock. 

Two things are conspicuous here : The lack of plants in the D columns 
(one in DO), and the comparatively large number in the O and the HD 
columns. These are not to be accounted for here altogether because of 
their vascular discoloration, because Table I, K, which represents where 
the 53 tubers (38.41 — per cent) fell which showed discoloration, does not 
account for the majority. Plainly these plants have been weakened by 
disease, their power of resistance lessened, and their vigor impaired. 
Examination showed that soil infection acted here to produce the disease, 
but a comparison of Table I, J, with Table I, A, reveals the great weak- 
ness acquired by these plants, which made them so easily attacked. 
These tubers were extreme cases, being stock that would not ordinarily 
get into commercial seed. The circumstances surrounding this lot of 
of seed tends to explain the true reason why farmers of the Greeley Dis- 
trict prefer to plant newly introduced seed every two years. 

Table I, K, represents the places in which that seed fell which showed 
pronounced vascular discoloration, according to the place they occupy 
in Table I, J. 



Mar. 17, 1919 Fusarium-Blight of Potatoes under I rrigation 295 

PEARL DISEASED SEED (TABLE I, L) 

In 1 917 one lot of seed, Pearl variety, was secured, each tuber of which 
showed positive vascular infection by species of Fusarium, as proven by 
isolation cultures. Conditions were generally more favorable for potato 
growth early in the 1917 season than they were in the 1916 season, and 
less favorable late in 1917 than in 1916. Table I, L, shows the perform- 
ance of this badly diseased stock. 

IDAHO RURAL (TABLE I, M) 

One lot of seed from Idaho, known as Idaho Rurals, and healthy 
throughout, were treated in the same manner. No tuber showed disease 
or infection in the vascular system. The performance of this lot of seed 
is illustrated in Table I, M. 

The similarity between Tables I , L, and I, M, is striking. The presence 
of plants in the HD columns is attributed to the unfavorable late season 
in 1917. This is taken to account for the uniform health as represented 
for the diseased Pearl variety in Table I, L. 

There is no reason to suppose that if mere chance had operated so as to 
have each seed fall where its twin fell, and vice versa, that the result 
would have been the same in any table. Each seed piece was sur- 
rounded by a different set of factors which operated to bring about 
disease or apparent health. For that reason it is unlikely that the results 
of a single year can be duplicated, though the average of similar years 
ought to strike a fair average. 

DISEASE RESISTANCE 

In the fall of 191 5 a field of potatoes was chosen upon which to conduct 
an experiment in disease resistance. It was one calculated to offer crop 
failure if one was reasonably possible. One end of the field was white 
with alkali, the soil was heavy, and drainage was poor. A portion of the 
field already had potatoes on it, supposedly of the Pearl variety. It 
presented a very ragged appearance owing to skips, diseased plants, 
and mixture. Two of the best-looking rows were selected to work upon, 
and all the diseased and mixed plants were staked. After frost the staked 
plants were taken out by hand, and the remaining healthy plants were 
harvested with a machine. In 191 6 this seed was planted on an adjoin- 
ing plot. All the plants came up healthy and with increased vigor. 
Some plants succumbed to blight during the season, but at least 90 per 
cent reached harvest. Again in 191 6 several rows were inspected, the 
diseased and mixed plants staked, and the healthy ones harvested as 
before. These were planted in 191 7 in a plot adjoining the one used in 
1 91 6. In comparison with other potatoes in the field, the vigor and 
health of the selected seed was notable. Very few diseased plants were 
to be found, and skips in the rows were rare. These plants promised 



296 Journal of Agricultural Research vol. xvi, No. » 

well for another year, when a mistake was made in watering by the farmer, 
the ground became water-logged, and the entire field was lost through 
blight in the mature stage. 

SOIL CONDITIONS AND IRRIGATION 

Soil conditions materially assist the plant or the fungus. If the 
ground is well moistened and loose when the seed is planted, a strong 
vigorous start may be obtained by the plant which will carry it well 
beyond the immediate reach of the fungus. It has been the common 
practice to withhold irrigation until the new tubers begin to set. If the 
plant can endure withholding artificial watering until the new tubers 
set, it is well to delay, but to postpone it until the plant is suffering 
acutely, brings it to a condition from which it never wholly recovers. 
The fungus will make headway in a drouthy plant. After irrigation 
water has been supplied, it is expedient to cultivate deeply, because 
irrigation water packs the soil tightly. Too great an application of 
water on heavy soil may leave the soil puddled, in which condition it 
must remain for several days before cultivation is possible. If this is 
accompanied by a rising soil temperature, the ill effects are increased. 
Occasionally a heavy rain will puddle the soil late in the season preced- 
ing harvest. This may occur on ground irrigated too late. In such an 
event it is common for the plants to blight generally and die. The 
damage now is not in the death of the foliage or the death of the plant, 
but in the rot which will attack the new tubers. This is a black-rot 
which may enter by way of the stolons, a common method, or through 
wound or lenticel. When such tubers have begun to rot, they are a total 
loss. If the rot has not been detected in the field, it may occur later 
in the bin, causing a worse trouble. All the tubers of a plant may not 
be attacked, however, and in such a case control consists in getting them 
out of the ground without delay. Early varieties in which the new 
tubers have time to come to full ripeness are more susceptible than late 
varieties. 

At this time correct irrigation practice is unknown. No rule can be 
formulated, because each piece of ground requires different treatment. 
During some years it is expedient to "irrigate up," meaning to water 
the field immediately after planting. If the soil is too dry, irrigation is 
necessary for germination and will carry the plant for the maximum 
length of time before rewatering. Harm results if the water applied in 
addition to the soil moisture present creates an excess. Irrigation of a 
plowed field in which nothing has been planted is impractical, owing to 
the absence of row ditches, and the fact that a certain time must elapse 
before anything can be planted. Cultivation should be given after each 
irrigation, so long as it can be done without damaging the plants below 
ground. Sandy soils need less cultivation than heavy soils. The best 



Mar. 17, 1919 Fusarium-B light of Potatoes under Irrigation 297 

judge of the soil on any farm is the farmer who has worked with it. 
Each parcel of land has its own pecularities, and advice on the handling 
of land should be specific. The very best conditions obtainable for the 
potato should prevail throughout the season, and so long as the farmer 
can control the environmental conditions no trouble is likely to result. 

CONTROL 

Control of Fusarium-blight has not been attained. Different methods 
have been employed, three of which offer reasonable hope of success. 

First, selection of plants whose progeny will offer resistance to the 
invading organisms. For this purpose, experiments are being carried 
out with standard accepted varieties known to be suited to the locality. 
It is possible to select for resistance and have it gradually evidenced in 
the performance of the plants, as in the field experiment noted above. 
That is satisfactory so long as some overwhelming circumstance does 
not intervene and wipe out the work of years. At best, resistance is but 
a relative thing. 

Second, control by seed treatment. The attempt has been made, not 
to kill something that may be on the seed as in the orthodox seed treat- 
ment, but to coat the cut seed with a preservative or fungicide which 
would remain vital throughout the season, preventing infection. Could 
this be done, it would offer an easy solution to the problem. Experi- 
ments were carried out in 191 7 to test out the effect of different solutions. 
None of them gave satisfaction. Several lots of potatoes were treated 
and planted on May 18, 191 8, with several different mixtures and com- 
pounds, all of which for some reason or other were suspected of having 
some possible preservation value. The seed used was the Rural variety, 
and was cut in the usual way. The method of application depended upon 
the nature of the fungicide, and this is noted under "Remarks" in Table 
II. One lot was treated with a spore suspension of F. oxysporum for 
comparison! On June 19, 191 8, a similar experiment was made with a 
few lots. The results of these experiments are given in Table II, and 
are the data taken from counting 600 plants. 



298 



Journal of Agricultural Research 



Vol. XVI, No. ii 



Table II. — Effect of various seed treatment on germination of Irish potatoes 
PLANTED MAY l8; COUNTED JUNE 1 5 



Treatment. 


Per- 
centage 
of ger- 
mina- 
tion. 


P.emarks. 


Nicotine sulphate 


75 

68 

90 



35 
40 

60 
70 
85 
97 


Dipped. 
Dipped. 
Dusted. 
Dusted, 
several 
Sprayed. 
Dusted. 
Dusted. 
Dipped. 
Sprayed. 
Dipped i 
Dipped i 


Solution 1 to 8,000. 


Bordeau mixture 


Formula 5-5-50. 

Seed remained unusually firm. 

Seed killed by treatment and rotted by 

organisms. 

Strong spore suspension. 
Some seed killed. 




Hypochlorous acid a 


Iron sulphate 


Lithurn carbonate 

Mercuric chlorid 


Thoroughly and quickfy rotted. 
Solution, 1 to 1,000. 


Mustard oil 




Controls 

Whole seed 


11 water. 

n 3 per cent solution of copper sulphate. 





PLANTED JUNE 19; COUNTED JULY 15 



Charcoal 

F. oxysporum. 
Onion juice . . . 
Control, cut. . . 
Whole seed. .. 



55 

88 

99 



Dusted. 

Sprayed. 

Dipped. Expressed juice of onions. 

Dipped in water. Average field performance. 

No treatment. 



<* Smith, J. L. et al. antiseptic action of hypochlorous acid and its application to wound treat- 
ment. In Brit. Med. Jonr., 1915, no. 2847, p. 129-136. July 24, 1915.) 

In the first planting the charcoal treatment gave better germination 
than the controls, but fell behind in the second planting. None of the 
others were worth the trouble of treatment. The whole seed gave much 
better stands and of more healthy vigorous plants. 

Third, in applying the best-known cultural practice to the propagation 
of the potato. For this no rules can be given. Each farmer should 
judge the condition of his land, its moisture content, tilth, and apparent 
needs. Rotation with grain and legumes is advisable, allowing the land 
to be cropped with alfalfa as many years as possible before potatoes are 
planted. Methods of irrigating and cultivation during the growing 
season should be investigated at the time for the field in question. 
Plate 41, A, shows afield planted with good seed, but owing to the dry- 
ness of the soil at planting time infection set in, and the fungus destroyed 
from 60 to 80 per cent of the seed, with the resulting poor stand. 

GENERAL DISCUSSION 

Infection of potatoes by F. oxysporum from the soil through the seed 
piece has never been recorded before, so far as is known. That it is of 
widespread general importance on alkali soils is believed, from conditions 
noted in several potato-growing regions of the West. In parts of the 



Mar. 17, 1919 Fusarium-Blight of Potatoes under Irrigation 299 

San Luis Valley, where so many unfavorable conditions are at work, 
owing to subirrigation and a high water table, the large majority of the 
potatoes show signs of this infection. Other investigators have found 
vascular infection of the seed to be the cause of much trouble, and the 
seriousness of that manner of infection elsewhere can not be judged from 
these experiments. In the Greeley District, where the Fusarium-blight 
has been so serious for many years, a fortunate change has taken place. 
This is regarded as being due to the introduction of other crops, potatoes 
being brought into the crop rotation only once in four years or more. 
The use of seed beans, sugar beets, grain, and alfalfa in the definite rota- 
tion is extending the time between the same crops with corresponding 
advantage to each. The potato was desirable as a high-priced crop, and 
still is, and the percentage of loss is less with rotation. 

Alkaline soils are a favorable medium for Fusarium spp. Pratt (12) 
found them to be abundant in virgin desert soils. The prolific and lux- 
uriant growth of species of Fusarium on alkaline media in pure cultures 
is an indication of what may be expected in part in alkaline soils where 
humus is abundant. In disease investigations of this kind it was found 
desirable to conduct the experiments as much as possible in the field, for 
the reason that conditions there came about naturally, and the response 
was immediate and proportionate. Greater care must be taken to note 
and record every conceivable change of condition. In the gross the 
changes from day to day are observable and are recorded by suitable 
instruments; but the changes that occur in the plant are more delicate 
and rapid than gross observations indicate. Each square foot of soil 
has its own conditions, not distinguishable from the adjoining square 
foot perhaps, but of sufficient difference to be felt by the plant. 

The plant feels these things and responds. If resistant stock is to be 
selected, these changes and conditions should be known, and the finer 
symptoms indicated by the plant must be recognized for the purpose 
of analysis. 

Temperatures of the soil are vital as regards infection. The critical 
temperature for infection has not been determined and it varies for the 
manner of infection. Seed-piece infection will occur at a considerably 
lower temperature than root infection. In the Carbondale District, at a 
higher altitude and in cooler soil than the Greeley District, only those 
plants show Fusarium-wilt symptoms which have decayed seed pieces. 
Usually the seed piece remains sound throughout the season there, and 
the plants are free from blight. In the Greeley District the soil temper- 
atures are higher, and the seed pieces are generally attacked. Root 
infection occurs with temperatures higher than the average. As the 
plants get larger and shade the ground, and the roots penetrate deeper 
the danger from root infection is lessened. 

There has been a belief that less blight occurs when the potatoes 
follow alfalfa than otherwise, and that the older the alfalfa was the 



300 Journal of Agricultural Research vol. xvi, No. « 

better would be the potatoes. The current reasons for this are many and 
varied, but the principal one given is that there is less blight in the 
soil. This may mean fewer fungus organisms in the soil, but that does 
not seem to be the case. In several instances potatoes grown from good 
stock on soil previously in alfalfa for nine years have been observed as 
badly diseased as the same seed on soil only one year in alfalfa. The 
organism was present as abundantly as ever, and wherever the condition 
of poor cultivation or heated soil was present, the disease was manifest. 
The true value of alfalfa preceding potatoes lies in the fertilizer incre- 
ment and mechanical improvement added to the soil, and not to any 
dearth of Fusarium spp. 

The use of whole seed is suggested, not as a means of controlling the 
blight, but of avoiding it. By the use of whole seed is meant not culls 
and other small potatoes, but tubers in good condition, well selected, 
and preferably of i^-ounce weight or greater. Whole seed has been 
many times condemned as yielding quantities of unmarketable small 
potatoes, and from the horticultural point of view this is a serious fault. 
Under irrigation, however, the writer believes that whole seed can be 
made to yield nearly as many marketable tubers as cut seed. The 
increased stand resulting and the fact that no labor is required in 
cutting would promise a return commensurate with the initial increased 
cost of the seed. In one commercial field in 191 8 the yield from whole 
seed was 100 per cent greater than that from cut seed of the same 
variety. This field is shown in plate 41, B. The cut seed was planted 
on the left and the whole seed on the right. The photograph was taken 
at midseason. Sandsten (13) believes that whole seed is preferable to 
cut seed in dry-land farming because it prevents seed-piece rot. 

SUMMARY 

The disease of potatoes in the field caused by Fusarium spp., princi- 
pally F. oxysporum, whereby death of the plant or decay of any part of 
it is brought about, is to be regarded as different phases of the same 
disease. For that reason it is desirable to apply a generally applicable 
name covering all stages. The term " Fusarium-blight " expresses this 
adequately. 

Two methods of infection are recognized: Infection from the soil of 
roots and root hairs, and infection of the seed piece, whereby the plant 
becomes diseased. The latter method is regarded as the most serious 
and responsive to environmental conditions in the Greeley district of 
Colorado. 

Three methods of control are suggested, none of which have yet 
proved wholly effective. First, selection for disease resistance, a method 
shown to be effective only to a minor degree. Second, superior cultural 
conditions for the potato plant, whereby it may always maintain a 
degree of resistance to pathogenic organisms through activity and 



Mar. 17. 1919 Fusarium-Blight of Potatoes under Irrigation 301 

health. Lengthened rotation periods employing other crops followed by 
alfalfa improve the nutritive and mechanical properties of the soil, while 
a judicious irrigation practice adapted to the particular field and season 
involved combined with suitable cultivation should constantly main- 
tain a steady and adequate, but never excessive, supply of moisture and 
insure suitable aeration. This is the method available to the farmer, so 
far as he knows what constitutes the best conditions for his land through- 
out a given season. Third, by the use of whole seed, free from wound 
or injury, thus preventing seed-piece infection, or at least maintaining 
the plant free from infection for the maximum length of time. The com- 
bination of the two last-named measures probably constitutes the most 
effective measures for control of Fusarium-blight. 

It is believed that more than one species of Fusarium is able to bring 
about each phase of the blight. F. oxysporum in pure culture under 
suitably controlled and natural conditions has been found to do this. 

Three general stages of the Fusarium-blight are recognized. First, 
the stage in which decay and death of the seed piece and new plant 
occurs before the new shoot emerges from the ground. Germination 
may or may not have occurred. Second, the later stage, in which the 
young plant shows many and diverse symptoms of infection by Fusa- 
rium spp., often resulting in death. Some of these manifestations are 
not fatal, and recovery is possible. Third, the mature stage, resulting 
in death, usually at an advanced state of growth, often with infection 
and decay of the new tubers. 

Different varieties of potatoes show marked variation in their behavior 
under the same general conditions. There is an inherent weakness in 
different strains of the Rural variety toward Fusarium-blight, accen- 
tuated by the conditions under which the seed was grown. The Pearl 
variety shows these weaknesses, but to a minor degree, unless brought 
to a poor condition by previous subjection to disease. 

Vascular infection of the seed is not the starting point of disease, but 
is one of the conditions assisting in bringing about decreased resistance 
to new infection from the soil. 

LITERATURE CITED 

(1) Appel, Otto, and WollEnweber, H. W. 

1910. GRUNDLAGEN EINER MONOGRAPHIE DER GATTUNG FUSARIUM (LlNK). 

In Arb. K. Biol. Anst. Land u. Forstw., Bd. 8, Heft 1, 207 p., 10 fig., 
3 pi. Verzeichnis der wichtigsten benutzen Schriften, p. 196-198. 

(2) Carpenter, C. W. 

191 5. SOME POTATO TUBER-ROTS CAUSED BY SPECIES OF FUSARIUM. In Jour. 

Agr. Research, v. 5, no. 5, p. 183-210, pi. A-B, 14-19- Literature, 
cited, p. 208-209. 

(3) Cromwell, R. O. 

I917. FUSARIUM-BLIGHT, OR WILT DISEASE, OF THE SOYBEAN. In Jour. Agr. 

Research, v. 8, no. n, p. 421-440, 1 fig., pi. 95. Literature cited, p. 

438-439- 



302 Journal of Agricultural Research vol. xvi, No. « 

(4) Jones, L. R., and Gilman, J. C. 

1915. THE CONTROL, OF CABBAGE YELLOWS THROUGH DISEASE RESISTANCE. 

Wis. Agr. Exp. Sta. Research Bui. 38, 70 p., 23 fig. Literature cited, 
p. 69-70. 

(5) Link, G. K. K. 

1916. A PHYSIOLOGICAL, STUDY OP TWO STRAINS OF FUSARIUM IN THErR CAUSAL 

RELATIONS TO TUBER-ROT AND WILT OF POTATO. Nebr. Agr. Exp. 

Sta. Research Bui. 9, 45 p., illus. Reprinted from Bot. Gaz., v. 62, 
no. 3, p. 169-209. 1916. 

(6) Manns, T. F. 

1911. the fusarium blight (wilt) and dry rot of the p/tato. Preliminary 
studies and field experiments. Ohio Agr. Exp. Sta. Bui. 229, p. 299- 
337, pi. 1-15. 

(7) Orton, W. A. 

1902. THE WLLT DISEASE OF THE COWPEA AND ITS CONTROL. In U. S. Dept. 

Agr. Bur. Plant Indus. Bui. 17, p. 9-22, 1 fig., 4 pi. 

(8) 

1010. cotton wnvr. U. S. Dept. Agr. Farmers' Bui. 333, 24 p., illus. 

(9) 

1914. potato wnyr, leaf-roll, and related diseases. U. S. Dept. Agr. Bui. 

64, 48 p., 16 pi. Bibliography, p. 44-48. 
(10) Pizzigoni, A. 

1896. cancrena secca ed unida DELLE pat ate. In Nuovo Gior. Bot. Ital., 

n. s. v. 3, fasc. 1, p. 50-53. 
11) Pratt, O. A. 

1916. A WESTERN PIELDROT OF THE IRISH POTATO TUBER CAUSED BY FUSARIUM 

radicicola. In Jour. Agr. Research, v. 6, no. 9, p. 297-309, pi. 34-37. 

(12) 

1918. SOIL FUNGI IN RELATION TO DISEASES OP THE IRISH POTATO IN SOUTHERN 

Idaho. In Jour. Agr. Research, v. 13, no. 2, p. 73-100, 4 fig., pi. A-B. 
Literature cited, p. 98-99. 

(13) Sandsten, E. P. 

1918. potato culture in Colorado. Colo. Agr. Exp. Sta. Bui. 243, 35 p. 
illus. 

(14) Sherbakoff, C. D. 

1915. fusaria op potatoes. N. Y. Cornell Agr. Exp. Sta. Mem. 6, p. 89-270, 

51 fig., 7 col. pi. Literature cited, p. 269-270. 

(15) Smith, Erwin F. 

1899. WILT disease of cotton, watermelon, and cowpea (neocosmospora 
Nov. gen.). U. S. Dept. Agr. Div. Veg. Phys. and Path. Bui. 17, 72 
p., 10 pi. 

(16) and Swingle, D. B. 

1904. THE DRY ROT OF POTATOES DUE TO FUSARIUM OXYSPORUM. U. S. Dept. 

Agr. Bur. Plant Indus. Bui. 55, 64 p., 2 fig., 8 pi. Literature cited, 
p. 61-62. 

(17) Wehmer, Carl. 

1897. UNTERSUCHUNGEN UBER KARTOFFELKRANKHEITEN. 2. ANSTECKUNGS 

VERSUCHE MIT FUSARIUM SOLANI. (DIE FUSARIUM-FAULE). /wCentbl. 

Bakt. [etc.], Abt. 2, Bd. 3, No. 25/26, p. 727-742, pi. io-n. 

(18) Wilcox, E. M., Link, G. K. K., and Pool, Venus W. 

1913. A dry rot of The irish potato Tuber. Nebr. Agr. Exp. Sta. Research 
Bui. 1, 88 p., 28 pi. Bibliography. 



Mar. 17, 1919 Fusarium-Blight of Potatoes under Irrigation 303 

(19) WoivLENWEBER, H. W. 

1913. PUZPARASITARE WELKEKRANKHEITEN DER KWTURPFLANZEN. In Ber., 

Deut. Bot. Gesell., Bd. 31, Heft 1, p. 17-34. 

(20) 

1913. studies on the fusarium PROBLEM. In Phytopathology, v. 3, no. 1, p. 
24-50, pi. 5. 



PLATE 37 
Effect of Fusarium -blight on seed pieces of potato: 

A. — Early Ohio seed pieces: Control above; pieces inoculated with F. oxysporum 
below. 

B. — Early Ohio plant. See piece inoculated with F. oxysporum. 

C. — Early Ohio seed pieces: Control (left) and inoculated (right) seed pieces. The 
control shows the method used in inoculation. 

D. — Seed piece well decayed, resulting from soil infection. 

E. — Seed-piece rot in field. 

3°4 



Fusarium-Blight of Potatoes under Irrigation 



PLATE 37 




Journal of Agricultural Research 



Vol. XVI, No. 11 



Fusarium-Blight of Potatoes under Irrigation 



Plate 38 




Journal of Agricultural Research 



Vol. XVI, No. 11 



PLATE 38 

A. — Inoculated and uninoculated stems of same potato plant. Stem at right 
shattered by F. oxysporum. 

B. — Potato plant (control), showing method of inoculating with wedge of melilotus 
stem. 

C. — Seed-piece rot in field. The young potato plant has not yet been attacked. 

D. — Potato plant naturally infected by F. oxysporum in the field. 



PLATE 39 
Potato stems showing seed-piece rot: 

A. — Stem split to show rotting due to organism entering through seed piece from 
soil. Note decay of roots from point of attachment outward. 

B. — Stem split to show slight discoloration at base where infection from soil-infected 
seed piece occurred. 

C. — Seed piece of potato plant shown in Plate 40, B. The center top leads to the 
center of decay. 

D. — Seed-piece rot in field. The seed piece is well decayed, but plant is unaffected 
and the roots are healthy. 



Fusarium-Blight of Potatoes under I rrigation 



Plate 39 




Journal of Agricultural Research 



Vol. XVI, No. 11 



Fusarium-Blight of Potatoes under I rrigation 



Plate 40 




Journal of Agricultural Research 



Vol. XVI, No. 11 



PLATE 40 
Potato plants affected by Fusarium-blight: 

A. — Potato plant late in season with rolled leaves. Fusarium blight. 

B. — Top of potato plant consisting of three stems. One leaf on one stem is wilted. 
See Plate 39, C. 

C— Potato plant of two stems, one at left showing Fusarium blight, or wilt caused 
by seed-piece infection; one at right healthy. 

D. —Plant with rolled leaves gradually dying from Fusarium blight. Severe case 
late in season. 



PLATE 41 

A. — A field of potatoes showing the result of unfavorable cultural and soil condi- 
tions, by which seed-piece rot destroyed 60 per cent of the stand. 

B. A field of potatoes planted with whole seed (rows to right) and cut seed (rows to. 
left) at midseason. The hills planted with whole seed gave a 100 per cent greater yield 
than those planted with cut seed. 



Fusarium-Blight of Potatoes under Irrigation 



Plate 41 







^.» 



%llliiiiA 




c ,->.' • " .■ TBI 



*s* 



,■«- ' 






?'4r. 



"1 




Journal of Agricultural Research 



Vol. XVI, No. 11 



